INFLUENCE OF WATER MANAGEMENT AND HYDROGEL USE ON ANNUAL AND PERENNIAL HERB GROWTH AND PRODUCTIVITY IN AN EXTENSIVE GREEN ROOF ENVIRONMENT

Author

Hunter Miles Christenson, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2025

Degree Name

Master of Science

Department

Plant, Soil, and Agricultural Systems

First Advisor

Walters, Alan

Abstract

AN ABSTRACT OF THE THESIS OFHunter Christenson, for the Master of Science degree in Plant and Soil Science, presented on February 28, 2025 at Southern Illinois University Carbondale.TITLE: INFLUENCE OF WATER MANAGEMENT AND HYDROGEL USE ON ANNUAL AND PERENNIAL HERB GROWTH AND PRODUCTIVITY IN AN EXTENSIVE GREEN ROOF ENVIRONMENTMAJOR PROFESSOR: Dr. S. Alan WaltersUrban agriculture is becoming increasingly important to provide sources of local food for urban residents. Extensive green roofs can be used to provide spaces for local agriculture in these urban environments, although extreme moisture and temperature conditions typically found in these systems can often be challenging for urban crop production. Therefore, two experiments were conducted on the Southern Illinois University – Carbondale (SIUC) extensive green roof that is located on top of the agriculture building. The first experiment evaluated the effects of a polyacrylamide hydrogel at 3 rates (0, 28, and 85 g per experimental unit), mulch (none and pine bark mulch), and irrigation frequency (1 L water per week or every two weeks per experimental unit) on the growth and productivity of two basil (Ocimum basilicum) varieties (‘Compact’ and ‘Italian Large Leaf’). The second experiment evaluated the effects of a polyacrylamide hydrogel at 2 rates (0 and 85 g per experimental unit), mulch (none and pine bark mulch), and irrigation frequency (1 L water per week or every two weeks per experimental unit) on the vigor, growth, and overwintering ability of two perennial culinary herbs, sage (Salvia officinalis) and thyme (Thymus vulgaris). For the basil experiment, weekly irrigation increased late-season plant vigor by 16%, fresh weight by 37%, and dry weight by 47% compared to biweekly watering. The use of pine bark mulch improved basil fresh weight by 19% and plant vigor by up to 32% compared to no mulch. Hydrogel application rates of 28 g and 85 g improved basil plant height by 42% and 32%, respectively, compared to no hydrogel, although no other growth parameters were affected.For perennial herbs, sage had greater vigor, overwinter survival, and overall suitability for extensive green roof environments compared to thyme. Sage exhibited a 96% overwinter survival rate, 15% higher than thyme, and 32% greater late-season plant vigor. Hydrogel application at 85 g reduced overwinter vigor by 22%, which was likely due to substrate heaving caused by hydrogel swelling, although survival rates were unaffected. Weekly irrigation increased late-season perennial herb vigor by 19% compared to biweekly watering, highlighting the importance of consistent water supply for growth and overwintering success. These results indicate that supplemental water is an important consideration for sustaining culinary herb production on extensive green roofs with the increasingly hot and dry conditions provided under the climate change scenarios projected for cities currently having temperate climates.